Emergency Generator Size Calculator
Determine the minimum generator size needed to power life-critical systems during power outages.
Emergency Priority Level
Life-Safety Systems
Essential Systems
Environmental Control
Security Systems
List of the Top 10 Best Emergency Generator:
Emergency Generator Sizing Guide
During disasters, your generator must reliably power critical systems. This calculator prioritizes:
- Life-support equipment (medical devices, oxygen)
- Basic survival needs (water, minimal refrigeration)
- Communication systems (emergency radios, phones)
- Environmental protection (sump pumps, minimal heating/cooling)
Emergency Power Tiers
| Tier | Generator Size | Typical Runtime* | Key Systems Supported |
|---|---|---|---|
| Basic Survival | 1,000-2,000W | 12-24 hours | Medical devices, phones, 2-3 lights |
| Extended Safety | 3,000-5,000W | 8-12 hours | Basic + fridge, sump pump, furnace fan |
| Full Preparedness | 7,500-10,000W | 5-8 hours | Extended + security, partial home circuits |
*Runtime estimates based on 5-gallon fuel tank at 50% load
Critical Load Prioritization
1 Life-Support Systems
- Medical equipment (oxygen, CPAP, dialysis)
- Emergency lighting (exit lights, flashlights)
- Communication devices (phones, radios)
2 Survival Essentials
- Refrigeration (medicines, basic food)
- Water pumps (well, pressure, sump)
- Minimal heating/cooling (life-threatening conditions)
3 Security & Comfort
- Security systems (alarms, cameras)
- Limited outlets (device charging)
- Partial HVAC (extreme weather)
Emergency Generator Types
Portable Inverter
Best for: Basic survival needs
Pros: Quiet, fuel-efficient, clean power
Cons: Limited capacity (1,000-3,500W)
Mid-Size Portable
Best for: Extended safety tier
Pros: Balance of power and portability
Cons: Requires manual operation
Standby Generator
Best for: Full preparedness
Pros: Automatic, whole-house capability
Cons: Expensive, requires professional install
Emergency Preparedness Tips
1. Fuel Storage
Store at least 72 hours of fuel (20+ gallons for gasoline). Use stabilizers and rotate stock every 3-6 months.
2. Transfer Switch
Install an emergency circuit transfer switch for quick, safe connection to critical circuits.
3. Load Sequencing
Manually stagger high-draw appliances (e.g., run fridge for 2 hours, then heating for 1 hour).
4. Backup Plans
Have battery backups for medical devices that can last until generator is started.
5. Maintenance Schedule
Test emergency generators monthly. Change oil every 50-100 hours of use.
6. Safety First
Never operate generators indoors or in garages. Keep CO detectors operational.
Frequently Asked Questions
What's the smallest generator that can power a CPAP machine?
A 1,000W inverter generator can run a CPAP (50-100W) plus small lights and phone charging. Choose an inverter model for clean power.
How do I power my well pump during an emergency?
Most 1/2 HP well pumps require 3,000-5,000W to start. Size your generator accordingly, and consider a soft-start kit to reduce surge.
Can I run my home's gas furnace with a portable generator?
Yes. Most gas furnace blowers use 800-1,500W. Ensure your generator can handle the starting surge (typically 2-3x running watts).
What's the safest way to connect emergency circuits?
Use a transfer switch installed by an electrician. Never use "suicide cords" to backfeed your panel - this is extremely dangerous.
How long can I continuously run my emergency generator?
Portable gasoline models need 8-12 hour cooldown periods after 12-24 hours of use. Standby units can run indefinitely with fuel.
Do I need to ground my portable emergency generator?
Yes, when powering home circuits. Use a grounding rod per NEC 250.34. Not required for extension cord use to individual appliances.
What's the best fuel for emergency storage?
Propane lasts indefinitely. For gasoline, use ethanol-free fuel with stabilizer (18-24 month shelf life vs. 3-6 months for regular gas).
How do I calculate fuel needs for a 72-hour outage?
Example: 5,000W generator at 50% load uses ~0.5 gal/hr. 0.5 x 72 = 36 gallons. Always add 20% buffer for inefficiency.
Can solar panels supplement my emergency generator?
Yes! Solar with battery storage can reduce generator runtime. Some systems automatically switch between power sources.
What maintenance does an emergency generator need?
Monthly: Start and run under load for 30 mins. Annually: Change oil, spark plug, air filter. Keep fuel fresh.